The Limits of Reason

Begley, Sharon, Newsweek

Byline: Sharon Begley

Why evolution may favor irrationality.

Women are bad drivers, Saddam plotted 9/11, Obama was not born in America, and Iraq had weapons of mass destruction: to believe any of these requires suspending some of our critical-thinking faculties and succumbing instead to the kind of irrationality that drives the logically minded crazy. It helps, for instance, to use confirmation bias (seeing and recalling only evidence that supports your beliefs, so you can recount examples of women driving 40mph in the fast lane). It also helps not to test your beliefs against empirical data (where, exactly, are the WMD, after seven years of U.S. forces crawling all over Iraq?); not to subject beliefs to the plausibility test (faking Obama's birth certificate would require how widespread a conspiracy?); and to be guided by emotion (the loss of thousands of American lives in Iraq feels more justified if we are avenging 9/11).

The fact that humans are subject to all these failures of rational thought seems to make no sense. Reason is supposed to be the highest achievement of the human mind, and the route to knowledge and wise decisions. But as psychologists have been documenting since the 1960s, humans are really, really bad at reasoning. It's not just that we follow our emotions so often, in contexts from voting to ethics. No, even when we intend to deploy the full force of our rational faculties, we are often as ineffectual as eunuchs at an orgy.

An idea sweeping through the ranks of philosophers and cognitive scientists suggests why this is so. The reason we succumb to confirmation bias, why we are blind to counterexamples, and why we fall short of Cartesian logic in so many other ways is that these lapses have a purpose: they help us "devise and evaluate arguments that are intended to persuade other people," says psychologist Hugo Mercier of the University of Pennsylvania. Failures of logic, he and cognitive scientist Dan Sperber of the Institut Jean Nicod in Paris propose, are in fact effective ploys to win arguments.

That puts poor reasoning in a completely different light. Arguing, after all, is less about seeking truth than about overcoming opposing views. So while confirmation bias, for instance, may mislead us about what's true and real, by letting examples that support our view monopolize our memory and perception, it maximizes the artillery we wield when trying to convince someone that, say, he really is "late all the time. …

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